This invention relates broadly to a method of controlling the physical condition of a target object of control such as its temperature and pressure, a temperature adjustor and a heat treatment apparatus using such a temperature adjustor. In particular, the invention relates to the technology of controlling the fluctuations in such a physical condition of a target object of a multi-input, multi-output interference system such as its temperature.
As disclosed in Japanese Patent Publication Tokkai 6-188462, for example, it has been known to use a temperature adjustor in the heat treatment of semiconductor wafers in the production process of semiconductor devices. When a semiconductor wafer is placed on a heat processing table to be heated in such a production process, a temperature adjustor is adapted to output signals based on temperatures detected by temperature sensors set for the heat processing table such that the temperature of the heat processing table will come to match a set temperature (target temperature) and the current to the heater for the heat processing table will be controlled through an electromagnetic switch or the like by these signals.
In such a heat treatment process for a semiconductor wafer, the temperature of the heat processing table must be controlled such that the semiconductor wafer can be subjected to a heat treatment uniformly at a desired temperature. For this purpose, a temperature control must be effected so as to correct the temperature difference between the semiconductor wafer and the heat processing table and the temperature fluctuations inside the wafer surface due to its positions.
For effecting such corrections, it is necessary to preliminarily carry out an adjustment work by using a test wafer having temperature sensors attached thereto, subjecting this test wafer to a heating process on the heat processing table, measuring the temperature distribution on the test wafer by this heating process and correcting the set temperature of the heat processing table or its detected (inputted) temperature inputted to the temperature adjustor such that the temperature of the test wafer will uniformly approach the desired temperature.
In the case of a multi-channel heat processing table having a plurality of temperature sensors and a plurality of heaters provided such that the currents to the heaters are individually controlled based on the temperatures outputted from these temperature sensors, the mutual interference among the channels makes it difficult to properly adjust the aforementioned set (or inputted) temperature. The operator's experience must be heavily depended upon and many trials and errors must be repeated.